In general, the space formed by the outer race, inner race (bearing race) and rolling elements of a rolling bearing is filled with a lubricant or grease to lubricate the rolling bearing. However, such a lubricant or grease is a liquid or semisolid material that can be scattered or fluidized during the operation of the bearing. In order to prevent the scattering or fluidization of the lubricant or grease, it is arc normally practiced to seal the rolling bearing with a seal plate or the like. Therefore, it has been difficult to lubricate a small-sized bearing for special purpose with a lubricant or grease.
In order to overcome these difficulties, it has recently been proposed to fill the space formed by the inner race, outer race and rolling elements of the bearing with a polymer containing a lubricant. For example, JP-B-63-23239 (The term "JP-B" as used herein means an "examined Japanese patent application") discloses an arrangement involving the filling of the space formed by the inner race, outer race and rolling elements of a bearing with a lubricant-containing polymer comprising a grease and a polyethylene (plastic grease).
During its operation, the above proposed rolling bearing filled with a lubricant-containing polymer allows the lubricant-containing polymer to gradually release the grease as a lubricating component so that it can be lubricated over an extended period of time.
However, this kind of a lubricant-containing polymer-filled rolling bearing is disadvantageous in that since the lubricant-containing polymer normally fills the entire part of the space formed by the outer race and the inner race excluding that occupied by the rolling elements, the rotation of the rolling elements is impeded or a powder that enters into the clearance between the rolling elements and the inner race and outer race is generated during the operation of the bearing to cause so-called biting or vibration of the entire shaft, thereby resulting in the drastic deterioration of the performance of the bearing. Furthermore, there are some cases that these troubles are accompanied by the rise in the temperature of the bearing.
In order to overcome these difficulties, JP-A-8-312652 (The term "JP-A" as used herein means an "unexamined published Japanese patent application")), which corresponds to U.S. Pat. No. 5,588,751, proposes an approach involving the formation of a layer made of a lubricating component between the cage and the rolling elements prior to the packing of a lubricant-containing polymer for the purpose of preventing the lubricant-containing polymer and the rolling elements from coming in direct contact with each other.
As such a lubricant-containing polymer-filled rolling bearing there is known a deep groove ball bearing comprising an inner race and an outer race the edge face of which are flush with each other, cylindrical roller bearing, self-aligning roller bearing or the like. In order to fill such a rolling bearing with a lubricant-containing polymer, a full-pack process is normally employed which comprises packing the lubricant-containing polymer in such an arrangement that the edge face of the bearing and the lubricant-containing polymer are flush with each other.
These lubricant-containing polymer-filled rolling bearings, including ordinary deep groove ball bearing, cylindrical rolling bearing and self-aligning roller bearing, have a structure such that the edge face of the inner race and the outer race are flush with each other and the case does not protrude from the edge face of these rings and thus can be relatively easily produced in the foregoing full-pack form.
However, referring to the foregoing rolling bearing having a lubricating component layer interposed between the rings and the rolling elements, there is no specifications concerning the predetermination of the kind of lubricating component to be used and the thickness of the lubricant layer, making it occasionally impossible to obtain improvement in lubricating properties. In particular, in the case where a lubricant is used as the lubricating component, a thick layer cannot be formed to occasionally result in an insufficient effect of improving the lubricating properties.